Ice and cold, described in both figurative and literal meanings, are throughout this poem. The cold climate of the speaker's sea voyages parallels the loneliness he feels. He feels trapped in this life but also suggests that he accepts it willingly because it is his life and part of God's plan. He feels drawn to life as a seafarer by the sea itself and by a sacred obligation to God. Therefore, he is resolved to this life (as it is God's plan for him), but is always conflicted because it is so difficult.
So, it is a fitting contradiction that the sea, so often described in terms of ice and cold, is what makes his heart beat again. It is as if his heart is frozen (in some metaphoric sense) until he re-enters the icy, lonely world of the sea. It is cold but symbolically gives him life.
The speaker suggests that his life is a spiritual calling. He answers his loneliness with faith in God's purpose. The poem can be viewed in two halves. The first half details the loneliness. The second half grows more religious as he looks to God (and heaven) for solace and comfort. He says that his "soul roams with the sea." If the sea life is his calling (and that which makes his heart beat), there is a strong connection between the sea and God.